The present invention relates generally to a heat conducting apparatus, and more particularly, to a thermal harness employing encased carbon based fibers and end attachment brackets for use in electrical and electronic applications.
Thermal Products, Inc. produces commercial thermal straps. These conventional straps use highly conductive carbon fiber weaves having ends encapsulated in copper. Unlike the present invention, these straps lack an outer casing material to not only restrain and protect the carbon fibers from damage and breaking, but also to encase and contain them in order to prevent fiber shedding and contamination of the highly electrically conductive carbon fibers which would not be desirable around electrical and electronic equipment. These straps also differ from the present invention by their use of metallic end fittings that add weight to the structure.
U.S. Pat. No. 5,077,637, issued Dec. 31, 1991, entitled xe2x80x9cSolid State Directional Thermal Cablexe2x80x9d discloses xe2x80x9ca solid state, directional, thermal cable including a bundle of elongated, flexible, carbon fibers having a high thermal conductivity in at least the longitudinal direction. Couplings at each end of the cable, bind together the fiber bundle and thermally engage the cable with objects having different temperatures, for transferring heat between the objects. The thermal cable may be used with a frame that supports a device to or from which heat is to be transferred. The thermal cable engages the frame at a first region proximate the device, and with a second region remote from the device and transfers heat between the first and second regions. The frame may include a composite material whose constituents have at least two different coefficients of thermal expansion, for establishing the overall coefficient of thermal expansion of the composite material. One of the constituents may have a negative coefficient of thermal expansion, and may be a carbon based material.xe2x80x9d
It is also stated that xe2x80x9cIn a preferred embodiment of this device, the frame includes a composite material whose constituents have at least two different coefficients of thermal expansion, for establishing the overall coefficient of thermal expansion for the composite material. One of the constituents may have a negative coefficient of thermal expansion and may include a carbon based material such as graphite or diamond.xe2x80x9d
U.S. Pat. No. 5,077,637 discloses that xe2x80x9cThe coupling means may be made from a composite of materials, such as metal and carbonxe2x80x9d and that the graphite fibers used in the thermal cable xe2x80x9cmay be enclosed by a flexible sleeve or sheathing 41 such as a plastic tube.xe2x80x9d U.S. Pat. No. 5,077,637 also discloses that xe2x80x9cCoupling 62 may be made from conventional materials or from a composite of materials which have a tuned coefficient of thermal expansion. Fibers 24d are inserted into the coupling, and the coupling is secured around the fibers by means such as crimping, potting the fibers in an adhesive or infiltrafing the fiber ends with molten metal. Fiber ends 15d are then cut and polished smooth.xe2x80x9d
However, nothing is disclosed or suggested in U.S. Pat. No. 5,077,637 regarding connection to components using an encapsulant (and/or end attachment) and a soft polymer, such as silicone. There is no disclosure or suggestion in U.S. Pat. No. 5,077,637 that the thermal harness may include an encapsulating membrane to contain the tows. There is no disclosure or suggestion in U.S. Pat. No. 5,077,637 that at each node or endpoint, the tows are fanned out and splayed into a silicone matrix. There is no disclosure or suggestion in U.S. Pat. No. 5,077,637 that encapsulant may be used to help apply pressure to the thermal harness end point. There is no disclosure or suggestion in U.S. Pat. No. 5,077,637 that fibers are supported by the end attachment and/or encapsulant and a silicone matrix, which keep the fibers from buckling. There is no disclosure or suggestion in U.S. Pat. No. 5,077,637 regarding the use of an outer casing for the thermal harness that comprises a tubular braided sleeve/jacket, or that the braided sleeve comprises a material such as metal wires, Kevlar(trademark)-like fibers, polyben-zimidazole (PBI) fibers, Zylon(trademark) fibers, plastic/textile fibers, or ceramic fibers. This outer braided casing acts as a containment for the carbon fibers and prevents any shedding or contamination of the highly electrically conductive carbon fibers around electrical components and electrical wiring.
There is no disclosure or suggestion in U.S. Pat. No. 5,077,637 regarding the use of an adhesion promoting material for promoting adhesion of the surfaces of individual filaments to the bonding material, or that the adhesion promoting material may be coating, finish, or sizing materials. There is no disclosure or suggestion in U.S. Pat. No. 5,077,637 regarding the use of bonding material which is a polymeric bonding material or a solder or brazing material. There is no disclosure or suggestion in U.S. Pat. No. 5,077,637 that the end fittings are made of either a polymeric resin reinforced graphite composite laminate, a carbon/carbon composite laminate, or a combination of one or the other of these composite laminates.
Accordingly, it would be advantageous to have an improved thermal harness using carbon based fiber and end attachment brackets that may be used in electrical and electronic applications.
The present invention provides for an improved thermal harness that comprises carbon based (graphite) fiber heat conducting elements coupled to either graphite composite, carbon/carbon composite, or metal end attachment brackets. An outer casing that preferably comprises a tubular braided sleeve surrounds the tubular heat conducting elements and eliminates possible contamination from the graphite fibers. The thermal harness may be advantageously used in electrical and electronic applications to dissipate heat from high temperature, heat-emanating components.
The thermal harness provides for a means for transferring heat from heat-emanating components to heat dispersion components in electrical and electronic equipment. High thermal conductivity carbon based fiber is used as the harness connecting the components. The connection is made using an encapsulant (and/or end attachment) and a xe2x80x9csoftxe2x80x9d polymer, such as silicone, to make contact with mating items. The harness may be used to directly transfer the heat to radiators and/or a xe2x80x9ccoldxe2x80x9d side of an electronic box. The thermal harness may be used to replace heat spreaders, thermal planes, and other mass-intensive thermal management devices.
The thermal harness significantly reduces weight of computer trays, thermal doublers, and heat pipe assemblies. Attachment using the end attachment brackets is also significantly lighter than conventional devices using copper or aluminum to encapsulate the fiber ends. Encapsulating the fiber in silicone, for example, allows many of the fiber ends to intimately make contact with adjoining surfaces, and may eliminate resistive losses found at conventional interfaces.
Use of the thermal harness reduces the weight of electronic assemblies by replacing currently-used components required to reduce junction temperatures. The thermal harness may attach directly to the heat generating components and creates a bridge to the heat dissipating components. A reduced-to-practice embodiment of the thermal harness is extremely lightweight since the carbon fiber has a density of approximately 1.7-2.3 g/cm3. The thermal harness provides efficient heat transfer and may eliminate thermal planes in space structures.
The thermal harness has carbon fiber bundled with groups of tows going to a heat-generating element. Encapsulant may be used to help apply pressure to the thermal harness end point. The encapsulant may also have provisions for fasteners, springs, or clips to secure the end of the harness. One advantage of this technique is the direct contact between individual fibers and the mating surface. Fibers are supported by the end attachment and/or encapsulant and the silicone matrix. In this manner, the fibers are kept from buckling.